Ab Initio Methods in First?Row Transition Metal Chemistry

Molecules containing 3d transition metals (TMs) are usually associated with versatile reactivity, partly due to their complicated electronic structures involving multiple close-lying spin states. An accurate description of different states is notoriously difficult and still a challenge for computational methodologies. Density functional theory, although repeatedly shown give less reliable results near-degeneracy problems, remains the workhorse explore reactivity TM complexes. Ab initio wavefunction theory has been lagging behind its high cost. However, tremendous efforts have put improve applicability over past few years, particularly local coupled cluster low-scaling multireference methods. In this mini-review, we highlight major advancements these ab techniques discuss recent applications in calculations state energetics first-row complexes, ranging from crossover compounds metalloproteins biomimetic complexes capable activating C?H bonds.